Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

2. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Receiver and evaporator

Compressor and condenser

Evaporator and compressor

3. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Equally

Unpredictable

4. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-56.6°C

-77.7°C

5. The capillary tube, as an expansion device, is used in

Room air conditioners

Water coolers

Domestic refrigerators

All of these

6. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Evaporator tubes

Capillary tubes

Refrigerant cooling tubes

7. The boiling point of ammonia is

-33.3°C

-30°C

-10.5°C

-77.7°C

8. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 9

1: 1

9: 1

9. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Saturated liquid

Superheated vapour

Wet vapour

10. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Three heat exchangers

Four heat exchangers

Page 2 of 4

11. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.376

0.6

0.67

12. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Piston type reciprocating

Axial

Centrifugal

13. Freon group of refrigerants are

Non-inflammable and toxic

Inflammable

Nontoxic and non-inflammable

Toxic

14. Cooling water is required for following equipment in ammonia absorption plant

Absorber

Condenser, absorber and separator (rectifier)

Condenser

Evaporator

15. Which of the following is not a desirable property of a refrigerant?

Low boiling point

High risibility with oil

Large latent heat

Good electrical conductor

16. Most thermostatic expansion valves are set for a superheat of

5°C

10°C

20°C

15°C

17. For obtaining high COP, the pressure range of compressor should be

Optimum

Low

High

Any value

18. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

A gas will never liquefy

19. Rating of a domestic refrigerator is of the order of

5 tons

0.1 ton

10 tons

40 tons

20. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Superheat the vapour

Page 3 of 4

21. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

22. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Rankine

Reversed Carnot

Rankine

23. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Brine

Ammonia

Freon

24. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

25. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

26. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

27. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

28. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

29. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always less than unity

Always more than unity

Any one of the above

30. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

8 bar

15 bar

2 bar

Page 4 of 4

31. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

32. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

33. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dew point temperature of air

Dry bulb temperature of air

Wet bulb temperature of air

34. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

At critical Temperature

35. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

36. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

37. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Positive

Zero

38. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

1.33

4.33

3.33

39. Which of the following cycles uses air as the refrigerant?

Ericson

Stirling

Bell Coleman

Carnot

40. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Normal cooling

Super-cooling

Sub-cooling or under-cooling

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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